1. Field of the Invention
The present invention relates to alkylphthalocyanine near-infrared absorbers. It also relates to recording and display materials fabricated with such near-infrared absorbers, including optical recording media (such as optical disks and optical cards), filters which absorb or screen near-infrared radiation (such as goggles), and liquid crystal display panels using near-infrared radiation.
2. Discussion of the Background
Near-infrared absorbers play an important role in optoelectronic applications such as information recording media, display media, sensors, and goggles.
Conventionally known near-infrared absorbers include cyanine dyes (Japanese Patent Laid-Open Nos. 46221/'81 and 112790/'83), phthalocyanine dyes (Japanese Patent Laid-Open No. 36490/'83), naphthoquinone dyes (Japanese Patent Laid-Open No. 15458/'85), anthraquinone dyes (Japanese Patent Laid-Open No. 291651/'86), and dithiol complexes (Japanese Patent Laid-Open No. 175693/'83).
However, the previously known dyes suffer from major disadvantages. Specifically, cyanine dyes are insufficient in fastness properties such as light resistance and thermal resistance. The absorption wavelength ranges of phthalocyanine dyes are as short as 600-700 nm. Anthraquinone and naphthoquinone dyes have a low molar extinction coefficient, on the order of several tens of thousands. Dithiol complexes are not sufficiently thermally stable and possess low molar extinction coefficients.
Thus, there remains a need for near-infrared absorbers which possess a sufficient degree of fastness properties, such as light resistance, weather resistance, and thermal resistance, and sufficiently high molar extinction coefficients.